Automotive electrochromic mirror reflective element cell assemblies typically include a front substrate and a rear substrate and an electrochromic medium sandwiched therebetween and contained within an interpane cavity, typically with the electrochromic medium sandwiched between a transparent electrically conductive coating on a second surface of the front substrate and a mirror reflector on a third surface of the rear substrate. In order to achieve a desired electrical surface resistance at the third surface of a third surface reflector mirror reflective element, a relatively thick coating of a base metal (such as a chromium coating or the like) is typically disposed at the third surface, and a less thick but still relatively thick and higher reflecting coating of an expensive metal, such as rhodium, palladium, platinum or ruthenium or the like, is overcoated at or over the base metal layer to provide the desired reflectivity and appearance for the mirror reflective element as viewed through the first surface of the front substrate. The thickness of particularly the base metal layer (such as chromium) may be such that, in order to achieve a desired low sheet electrical resistance for the overall mirror reflector for the likes of larger area exterior electrochromic mirror reflective elements such as used for the likes of mid to large sized SUVs, trucks and/or minivans and/or the like, the base metal layer may exhibit roughness or unevenness in its outer surface, thus requiring an even thicker (and thus potentially more costly) overcoat of the likes of ruthenium or the like so that the overall visible light reflectivity of the mirror reflective element is enhanced and is not deleteriously impacted by surface roughness.